Conventionally, a shaft sealing mechanism for reducing the amount of leakage of fluid leaked from a high-pressure side to a low-pressure side is disposed around a rotating shaft of a steam turbine or a gas turbine, in order to reduce a loss of driving force. Such a shaft sealing mechanism has an annular seal structure in which multiple layers of thin-plate seal pieces in flat plate shapes with their width dimensions being in the rotating shaft direction are arranged in the circumferential direction of the rotating shaft. Outer-circumferential-side proximal ends of the thin-plate seal pieces are fixed to an annular seal housing while inner-circumferential-side distal ends the thin-plate seal pieces are in sliding contact with the outer circumferential surface of the rotating shaft at a predetermined preload. This enables the shaft sealing mechanism to partition the surrounding space of the rotating shaft into a high-pressure-side region and a low-pressure-side region with the boundary formed by a large number of the thin-plate seal pieces arranged annularly on the outer side in the radial direction of the rotating shaft.
Hence, while the rotating shaft is not rotating, the inner-circumferential-side distal ends of the thin-plate seal pieces are in contact with the outer circumferential surface of the rotating shaft at the predetermined preload. On the other hand, while the rotating shaft is rotating, the thin-plate seal pieces are warped by pressure difference due to relative positional difference in pressure distribution between the upper and lower surfaces of the thin-plate seal pieces and by dynamic pressure effect of the fluid generated by the rotation of the rotating shaft, and accordingly, the inner-circumferential-side distal ends of the thin-plate seal pieces are floated up from the outer circumferential surface of the rotating shaft and brought into a noncontact state. This prevents abrasion and heat generation of the thin-plate seal pieces and the rotating shaft. Note that the surfaces of the thin-plate seal pieces facing the rotating shaft are referred to as the lower surfaces, and the surfaces thereof opposite from the lower surfaces are referred to as the upper surfaces.
Such a conventional shaft sealing mechanism has been disclosed, for example, in Patent Document 1.